Method for magnetic burst testing of large electric motors with portable tester powered by a domestic wall outlet

ABSTRACT

A method for magnetic/impedance burst testing of large electric motors to determine broken rotor bar defect. The method providing a portable tester and includes a Signal Processor, a single-phase power source VAC, an AC/DC boost converter connected to the power source, at least one energy storage device connected to the AC to DC boost converter, a Pulse Width Modulated drive module (PWM) connected to the at least one energy storage device, and a series of at least three switches (IPM) using switch/level boost-type PWM rectification. The burst test is repeated until a full rotation of magnetic angles are tested and recorded with the Signal Processor. Rotor impedance versus magnetic angle of the full rotation is verified in order to check for failure, and broken rotor bar defect is determined when a shift in measured stator&#39;s impedance/admittance level for any of the given magnetic angles is identified by the Signal Processor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/849,854, filed Dec. 21, 2017. The above-referenced patent applicationis incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to a method for magnetic burst testing of largemotors. More particularly, to a method for magnetic burst testing oflarger motors with a portable tester powered by a domestic wall outlet.

Description of the Related Technology

There is difficulty in delivering sufficient motor current to test largeindustrial motors using a portable tester. Prior to this invention, thetester needed to be powered by a two or three phase outlet of 220V orhigher. With this invention, the tester can run broken rotor bar testsusing a single-phase outlet of just 117/120 Volts.

SUMMARY

This invention provides a small portable tester powered from a walloutlet in the 15-20 amperes range to provide sufficient test current(5-10% of nameplate) to test industrial motors of several thousandhorsepower for the broken rotor bar defect. In a first aspect, a methodfor magnetic/impedance burst testing of large electric motors isprovided. The method includes providing a portable tester that providesa Signal Processor, a single-phase power source VAC, an AC to DC boostconverter connected to the power source, at least one energy storagedevice connected to the AC to DC boost converter, a pulse widthmodulated drive (PWM) module connected to the at least one energystorage device, and a series of at least three switches (IPM) usingswitch/level boost-type PWM rectification, the IPM connected to both the3 legs of the large electric motor and the PWM drive.

The method includes programming the PWM drive with a desired duration ofoutput burst with the Signal Processor, programming the PWM drive withan initial magnetic test angle with the Signal Processor, programmingthe PWM drive with a test frequency for magnetic angle reversals withthe Signal Processor, programming the Programmable Gain Amplifier withthe Signal Processor to optimize the signal gain in order to preventvoltage and current signal clipping, controlling the PWM drive modulewith the Signal Processor to control the amplitude, magnetic angle andreversal frequency applied to the ACIM, controlling the boost converterwith the Signal Processor to limit/throttle the maximum power drawn fromthe single-phase AC source and the power delivered to the large energystorage device to maximally charge the energy storage device,controlling the series of switches (IPM) with the CCP to prevent crowbarof the DC Buss by adding dead-time to the PWM signals and interlockingout unsafe PWM conditions, controlling the CCP with the PWM drive moduleto pass through only safe PWM drive conditions, controlling the chargingof the at least one energy storage device with the boost converter to amaximum working voltage, sending an enable signal to the PWM drive tobegin burst output from the Signal Processor, sampling a stream ofmeasured voltage and/or currents of at least one of the motor legsduring burst output with a voltage transducer and a current transducerrespectively, which converts from analog to a digital A/D Converterdigital number with the A/D Converter, adjusting the PWM drive with theset point level and measured voltage and/or current to maintain adesired burst level in order to compensate for sinking voltage of the atleast one energy storage device applied to the programmed voltage and/orcurrent level applied to the motor with the Signal Processor, recordingthe stream of digital numbers with the Signal Processor, calculating, atthe end of each burst, rotor characteristics that include impedance,admittance, instantaneous power, voltage and currents for the previouslyapplied magnetic test angle with the Signal Processor, recharging the atleast one energy storage device with the boost converter until themaximum working voltage is attained, advancing the magnetic angle by Ndegrees to measure the response of each set of rotor bars that are inthe line given magnetic angle and verify the response is the same forall magnetic angles with the Signal Processor, repeating the burst testN number of times until a full rotation of magnetic angles are testedand recorded with the Signal Processor, verifying, with the SignalProcessor, rotor impedance versus magnetic angle of the full rotation inorder to check for failure, and determining failure by identifying ashift in measured stator's impedance/admittance, harmonic orsub-harmonic level for any of the given magnetic angles by the SignalProcessor.

A second aspect of the invention further includes using the recordedvoltage and current samples to calculate the response of the rotor barsstimulated by the burst pulse for the given magnetic angle setting,harmonics, pulsation, wherein intermittently connected rotor bar defectare identified as well.

In a third aspect of the invention if the response for a given magneticangle is different than all the other measured magnetic angles, then theconstruction of the rotor is not symmetrical, indicating a failure inone of the rotor bar sets probed by the magnetic angle as shown by thedeviation from the normalized measurements.

In another aspect of the invention, the power source is a domestic walloutlet and/or a battery, and wherein the at least one energy storagedevice is a DC link capacitor and/or battery,

In another aspect of the invention, the PWM drive with a test frequencyfor magnetic angle reversals is preferably in the range from 1 Hz to10,000 Hz.

In another aspect of the invention, the maximum working voltage isrequired to charge the at least one energy storage device so that theboost converter can supply a power burst up to 8 KW.

In another aspect of the invention, the stimulus burst applied to thestator coils is magnetically coupled to the rotor coil, the response ofthe rotor coil to the stimulus burst is recorded, and wherein there is ashort transient response that dies out in about 2½ cycles, which is thenfollowed by a steady state response of the rotor to the burst pulse.

In another aspect of the invention, in addition to the transformercoupled impedance of the rotor as measured by the stator, the harmonicand sub-harmonic response of the rotor to the burst are measured, andwhen the magnetic angle of the burst pulse is rotated to probe the rotorbars that the magnetic field passes through.

In a final aspect of the invention, by rotating the magnetic field,different rotor bar sets are probed, and wherein a response of a goodrotor bar set responding to a burst pulse at one magnetic field anglesimulating them is identified as being different than that of brokenrotor bar set probed with the magnetic angle burst pulse that stimulatesthem instead.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofembodiments are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 illustrates a block diagram of a system for the magnetic bursttesting of large electric motors according to the present invention,

FIG. 2A illustrates a first portion of a flow diagram of a method forthe magnetic burst testing of large electric motors according to thesystem of FIG. 1,

FIG. 2B illustrates a continuation of the flow diagram introduced inFIG. 2A with continuity provided by the continuity identifier A.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

Various examples will now be described more fully with reference to theaccompanying drawings in which some examples are illustrated. In thefigures, the thicknesses of lines, layers and/or regions may beexaggerated for clarity.

Accordingly, while further examples are capable of various modificationsand alternative forms, some particular examples thereof are shown in thefigures and will subsequently be described in detail. However, thisdetailed description does not limit further examples to the particularforms described. Further examples may cover all modifications,equivalents, and alternatives falling within the scope of thedisclosure. Like numbers refer to like or similar elements throughoutthe description of the figures, which may be implemented identically orin modified form when compared to one another while providing for thesame or a similar functionality.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, the elements may bedirectly connected or coupled or via one or more intervening elements.The terminology used herein for the purpose of describing particularexamples is not intended to be limiting for further examples. Whenever asingular form such as “a,” “an” and “the” is used and using only asingle element is neither explicitly or implicitly defined as beingmandatory, further examples may also use plural elements to implementthe same functionality. Likewise, when a functionality is subsequentlydescribed as being implemented using multiple elements, further examplesmay implement the same functionality using a single element orprocessing entity. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when used,specify the presence of the stated features, integers, steps,operations, processes, acts, elements and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, processes, acts, elements, componentsand/or any group thereof.

Unless otherwise defined, all terms (including technical and scientificterms) are used herein in their ordinary meaning of the art to which theexamples belong. The description and drawings merely illustrate theprinciples of the disclosure. Furthermore, all examples recited hereinare principally intended expressly to be only for pedagogical purposesto aid the reader in understanding the principles of the disclosure andthe concepts contributed by the inventor(s) to furthering the art. Allstatements herein reciting principles, aspects, and examples of thedisclosure, as well as specific examples thereof, are intended toencompass equivalents thereof.

System for Magnetic Burst Testing

FIG. 1 shows a block diagram of a portable system 100 for the magneticburst testing (broken rotor bar) of large electric motors 110. Thecomponents shown within the system 100 are generally packaged into arelatively small, portable testing unit (actual unit not shown) that canbe easily transported to an equipment site. The large electric motors tobe burst tested are typically AC induction motors (ACIM's) 110 that aredifficult to move. Thus, the portable system 100 of the presentinvention provides an advantage to the industry for testing largestationary ACIM's 110 and an advantage where the test site only has anordinary single-phase domestic power outlet of just 117/120 Volts,negating the need for a two or three phase outlet of 220V or higher andthe associated specialized multi-phase high current ‘industrial’extension cord needed to connect the tester to the two or three phaseindustrial power outlet.

The system 100 further provides an input power source 140 that isconnected to an AC to DC Boost Converter 130. The input power source 140is typically a single-phase AC power source at line voltage or 110-115VAC. The AC to DC Boost Converter 130 is connected to at least oneenergy storage device 150. The power source 140 may alternately be abattery 140 suitable for use in the application. That is, a battery 140having the capacity to repeatedly charge the energy storage device 150until a maximum working voltage is maintained. Once the maximum workingvoltage for the energy storage device has been reached, the IPM 160 cansimultaneously draw power from both the energy storage device 150 andthe boost converter 130 to supply a power burst up to 8 KW for testing amagnetic angle. This enables one to test all classes of medium voltageACIM's. The energy storage device 150 may need to be recharged to themaximum working voltage multiple times during a set of tests for brokenrotor bar defect. As such, the battery capacity is configured to handlethis required load energy for multiple recharges.

Adding an AC to DC Boost Converter 130 to the at least one energystorage device 150 enables higher DC bus link voltage operation at lowerAC line voltages and increases the stored energy in the energy storagedevice 150. One type of energy storage device 150 could be a DC Bus LinkCapacitor 150. Alternately, a high discharge rate battery 150 mayprovide a suitable energy storage device 150 for purposes of theinvention.

The stored energy in the Bus Link Capacitor is determined by the basicequation E=½ C*(V){circumflex over ( )}2. So for example, adding the ACto DC Boost Converter to the DC bus link capacitor enables higher DC buslink voltage operation at lower AC line voltages and increases thestored energy in bus link capacitor. Consequently, with the ability tostore more energy in the energy storage device, larger ACIM's can betested using a momentary current burst test at a given magnetic angle.

By increasing the DC bus link capacitor voltage with the boostconverter, the voltage margin to drive the necessary test currentthrough the motor can be provided as the energy is drained from the dcbus capacitor during a burst test. The duty cycle of the drive PWM canbe adjusted to maintain constant motor drive test current as the energyis drained from the DC bus link during the burst test of a givenmagnetic test angle. The power provided by a 20 A 110V outletsupplemented by the stored energy in the DC bus link capacitor enablessufficient current [typically 5-10]% of nameplate current through themotor for a momentary burst to detect broken rotor bars in ACIM's.

The at least one energy storage device 150 is connected to anIntelligent Power Module (IPM) 160. The IPM 160 is basically a bundle offixed power switches that are connected to the 3 legs of the ACIM 110.In addition, the IPM 160 may include a Cross-Conduction Preventer 180 aswell as high and low side drivers for each power switch, isolated powerconverters for internal components, fault detection circuitry as well asscaled current and voltage outputs for each output leg (U, V, W) thatcould be connected to a Programmable Gain Amplifier (PGA) PGA 185. Inaddition to being connected to the ACIM, the IPM 160 is connected to theProgrammable Gain Amplifier (PGA) 185 either by additional current senseresistors and voltage dividers inserted on each leg U, V and W or byscaled/conditioned current and voltage outputs provided by the IPM 160.

The programmable-gain amplifier (PGA) 185 is an electronic amplifier(typically an operational amplifier) whose gain can be controlled byexternal digital or analog signals. Here, the PGA 185 receives bothvoltage and current signals being fed by the IPM 160 to the ACIM. ThePGA 185 adds gain to the signal before entering into an A/D converter190. The A/D converter 190 provides an input that is fixed in range.Therefore, the PGA 185 is required in order to boost gain for singlelevel compensation depending on the size and power requirements of theACIM to be tested and the range and resolution of the chosen A/D 190.

A pulse width modulated drive module (PWM) 170 is connected to a seriesof at least three switches in the (IPM) 160 using switch/levelboost-type PWM rectification. The amplitude of the 3 pairs of PWMs 170are programmed by the DSP for a given magnetic angle N with the Uchannel set to sin(N), V set to sin(N+120) and W set to (N+240). Duringthe Burst test for each magnetic angle, the DSP will reverse the U, Wand V amplitudes at a given reversal frequency either by applying a[1,−1] amplitude modifier or sinusoidal amplitude modifier at thereversal frequency rate. The IPM is connected to both the (3) legs ofthe ACIM 110 and the PWM 170. The PWM 170 is connected to the IPM 160through a Cross Conduction Preventer (CCP) 180. The CCP 180 is providedas a safety. It prevents severe damage to the system 100 if the PWM 170is programmed incorrectly. The cross-conduction preventer ensures thateach set of switches in the IPM forming a half-bridge converter havesufficient dead-time added to the PWM signals to preventcross-conduction of the half-bridge converter switches. The dead-timeadded will depends upon the storage time characteristics of theparticular device [FET, IGBT, GTO, etc.] implemented in the IPM 160.This “dead time” must be of sufficient duration to ensure that the “on”states of the two power switches do not overlap under any conditions.

Finally, a Signal Processor 120 is provided in order to control thefunction of system 100. The Signal Processor 120 controls both the PWM170 and AC to DC Boost Converter 130 based on feedback received from theA/D converter 190 and from the energy storage device 150. The functionof the Signal Processor may be provided by a single dedicated processor,by a single shared processor, or by a plurality of individualprocessors, some of which or all of which may be shared.

However, the term “processor” or “controller” is by far not limited tohardware exclusively capable of executing software, but may includedigital signal processor (DSP) hardware, network processor, applicationspecific integrated circuit (ASIC), field programmable gate array(FPGA), read only memory (ROM) for storing software, random accessmemory (RAM), and non-volatile storage. Other hardware, conventionaland/or custom, may also be included.

In order to carry out the function of the system, the PWM is programmedwith a desired duration of output burst by the Signal Processor. Thedesired duration programmed into the PWM depends on the size and powerrequirements of the ACIM to be tested. The PWM is further programmedwith an initial magnetic test angle by the Signal Processor and with atest frequency for magnetic angle reversals by the Signal Processor. Thetest frequency for magnetic angle reversals is preferably in the rangefrom 1 Hz to 10,000 Hz. The test frequency includes a large rangebecause it depends on iron depth penetration of the magnetic field,which varies with the size of ACIM. The magnetic field of a lowerreversal test frequency penetrates deeper into the iron of a rotorwhereas a higher reversal test frequency only affects the top surface ofa rotor much as the ‘skin depth’ penetration of a RF field decreaseswith increasing frequency.

Finally, the PGA is programmed by the Signal Processor to optimize thesignal gain in order to prevent voltage and current signal clipping. Inaddition, the PGA gain optimizes the signal to noise ratio of the signaland reduce quantization artifacts. The PWM is controlled by the SignalProcessor to control the amplitude, magnetic angle and reversalfrequency applied to the ACIM. In addition, the boost converter iscontrolled with the Signal Processor to limit/throttle the maximum powerdrawn from the single-phase AC source/battery 140 and the powerdelivered to the large energy storage device 150 to maximally charge theenergy storage device.

The series of switches in the IPM is controlled with the CCP to preventcrowbar of the DC Buss by adding dead-time to the PWM signals andinterlocking out unsafe PWM conditions. The CCP is controlled with thePWM drive module to pass through only safe PWM drive conditions.Finally, the charging of the at least one energy storage device iscontrolled by the boost converter to obtain a maximum working voltage.

An enable signal from the Signal Processor is first sent to the PWMdrive to begin burst output from the Signal Processor. Then, a stream ofmeasured voltage and/or currents of at least one of the motor legsduring burst output with a voltage transducer and a current transducerrespectively are sampled. The sampled stream is converted from an analogmeasured value to a digital number within the A/D Converter. A resistivevoltage divider network placed on each motor leg may be provided toscale down the burst test voltage to a level that an analog to digitalconverter can sample using the Signal Processor. A series resistor, halleffect device or current transformer placed on each motor leg may beprovided to convert the test current to a proportional voltage that ananalog to digital converter can sample using the Signal Processor.

The PWM drive is adjusted with a set point level and measured voltageand/or current to maintain a desired burst level. This is essentially anelectrical feedback loop that is used to push the output drive to adesired set-point in order to compensate for sinking voltage of the atleast one energy storage device 150 applied to the programmed voltageand/or current level applied to the motor with the Signal Processor 120.The stream of digital numbers is then recorded within the SignalProcessor.

The stimulus burst applied to the stator coil of the ACIM ismagnetically coupled to the rotor coil. The response of the rotor coilto the stimulus burst is then recorded as previously disclosed. There isa short transient response thereafter that dies out in about 2½ cycles.This is followed by a steady state response of the rotor to the burstpulse. Here, after the transient dies out the system then focuses on thesteady state response.

At the end of each burst, rotor characteristics that include impedance,admittance, instantaneous power (I squared r), voltage and currents forthe previously applied magnetic test angle are calculated within theSignal Processor. The at least one energy storage device is recharged bythe boost converter until the maximum working voltage is attained onceagain. The Signal Processor advances the magnetic angle by N degrees tomeasure the response of each set of rotor bars that are in the linegiven magnetic angle and verify that the response is the same for allmagnetic angles. The Signal Processor repeats the burst test by N numberof times until a full rotation of magnetic angles are tested andrecorded in a memory within the Signal Processor.

The Signal Processor verifies rotor impedance versus magnetic angle ofthe full rotation in order to check for failure. Broken rotor bar defectis determined when a shift in measured stator's impedance/admittance(Resistance and inductance), for any of the given magnetic angles isidentified by the Signal Processor. In an alternate embodiment, therecorded voltage and current samples used to calculate the response ofthe rotor bars stimulated by the burst pulse for the given magneticangle setting, may provide harmonic or sub-harmonic level harmonics,pulsation, etc. That is, not only impedance could be verified, but forintermittently connected rotor bar as well

By rotating the magnetic field, different rotor bar sets may be probed.A response of a good rotor bar set responding to a burst pulse at onemagnetic field angle simulating them is identified as being differentthan that of broken rotor bar set probed with the magnetic angle burstpulse that stimulates them instead. Consequently, it is clear thatdifferent responses are obtained between a good rotor bar responseversus a bad rotor bar response.

Further, if the response for a given magnetic angle is different thanall the other measured magnetic angles, then the construction of therotor is not symmetrical. As such, a failure in one of the rotor barsets probed by the magnetic angle is shown by the deviation from thenormalized measurements. Consequently, rotor porosity problems couldalso be detected.

In addition to the transformer coupled impedance of the rotor asmeasured by the stator, the harmonics and sub-harmonic response of therotor to the burst are measured. Here, the magnetic angle of the burstpulse is rotated to probe the rotor bars that the magnetic field passesthrough. Consequently, additional harmonics and sub-harmonic responsecan be beneficial in determining faults.

Method for Magnetic Burst Testing

A method 300 for magnetic/impedance burst testing of large electricmotors will now be disclosed. The method 300 includes providing 310 theportable tester having the Signal Processor, the single-phase powersource VAC, the AC to DC boost converter connected to the power source,at least one energy storage device connected to the AC to DC boostconverter, the pulse width modulated drive (PWM) module connected to theat least one energy storage device, and the series of at least threeswitches (IPM) using switch/level boost-type PWM rectification, the IPMbeing connected to both the 3 legs of the large electric motor and thePWM drive.

The method further provides the following programming steps that arerequired in order to carry out the method. They include a step ofprogramming the PWM drive 320 with a desired duration of output burst,programing the PWM drive 330 with an initial magnetic test angle,programing the PWM drive 340 with a test frequency for magnetic anglereversals, and programming the Programmable Gain Amplifier 350 tooptimize the signal gain in order to prevent voltage and current signalclipping. All of the aforementioned programming steps are carried out bythe Signal Processor.

The method provides the following controlling steps that are required tocontrol the method. They include a step of controlling the PWM drivemodule 360 to control the amplitude, magnetic angle and reversalfrequency applied to the ACIM, controlling the boost converter 370 withthe Signal Processor to limit/throttle the maximum power drawn from thesingle-phase AC source and the power delivered to the large energystorage device to maximally charge the energy storage device,controlling the series of switches (IPM) 380 with the CCP to preventcrowbar of the DC Buss by adding dead-time to the PWM signals andinterlocking out unsafe PWM conditions, controlling the CCP 390 with thePWM drive module to pass through only safe PWM drive conditions, andcontrolling the charging of the at least one energy storage device 400with the boost converter to a maximum working voltage.

The method then provides a step of sending an enable signal 410 to thePWM drive to begin burst output from the Signal Processor. Further, astep of sampling a stream of measured voltage and/or currents of atleast one of the motor legs 420 during burst output with the voltagetransducer and the current transducer respectively is provided. Thisconverts from the analog to the digital A/D Converter digital numberwith the A/D Converter.

Next, a step of adjusting 430 the PWM drive with the set point level andmeasured voltage and/or current to maintain a desired burst level(electrical feedback loop to push the output drive to a desiredset-point) in order to compensate for sinking voltage of the at leastone energy storage device applied to the programmed voltage and/orcurrent level applied to the motor with the Signal Processor is carriedout. A step of recording the stream of digital numbers 440 with theSignal Processor is carried out.

The method includes calculating, at the end of each burst, rotorcharacteristics 450 that may include impedance, admittance,instantaneous power, voltage and currents for the previously appliedmagnetic test angle with the Signal Processor,

Subsequently, a step of recharging 460 the at least one energy storagedevice with the boost converter until the maximum working voltage isattained is then undertaken. In step 470, advancing the magnetic angleby N degrees to measure the response of each set of rotor bars that arein the line given magnetic angle and verify the response is the same forall magnetic angles with the Signal Processor is started. In step 480,repeating the burst test N number of times until a full rotation ofmagnetic angles are tested and recorded with the Signal Processor isstarted.

In step 490 verifying, with the Signal Processor, rotor impedance versusmagnetic angle of the full rotation in order to check for failure isinitiated, and finally, in step 500 determining failure by identifying ashift in measured stator's impedance/admittance, harmonic orsub-harmonic level for any of the given magnetic angles is accomplishedby the Signal Processor.

A block diagram may, for instance, illustrate a high-level circuitdiagram implementing the principles of the disclosure. Similarly, a flowchart, a flow diagram, a state transition diagram, a pseudo code, andthe like may represent various processes, operations or steps, whichmay, for instance, be substantially represented in computer readablemedium and so executed by a computer or processor, whether or not suchcomputer or processor is explicitly shown. Methods disclosed in thespecification or in the claims may be implemented by a device havingmeans for performing each of the respective acts of these methods.

Furthermore, the following claims are hereby incorporated into thedetailed description, where each claim may stand on its own as aseparate example. While each claim may stand on its own as a separateexample, it is to be noted that a dependent claim may refer in theclaims to a specific combination with one or more other claims.

Other examples may also include a combination of the dependent claimwith the subject matter of each other dependent or independent claim.Such combinations are explicitly proposed herein unless it is statedthat a specific combination is not intended. Furthermore, it is intendedto include also features of a claim to any other independent claim evenif this claim is not directly made dependent to the independent claim.

What is claimed is:
 1. A method for magnetic/impedance burst testing ofelectric motors comprising: providing a portable tester that provides aSignal Processor, a single-phase power source VAC, an AC to DC boostconverter connected to the power source, at least one energy storagedevice connected to the AC to DC boost converter, a pulse widthmodulated drive (PWM) module connected to the at least one energystorage device, and a series of at least three switches (IPM) usingswitch/level boost-type PWM rectification, the IPM connected to both the3 legs of the large electric motor and the PWM drive, the methodcomprising: programming the PWM drive with a desired duration of outputburst with the Signal Processor; programming the PWM drive with aninitial magnetic test angle with the Signal Processor; programming thePWM drive with a test frequency for magnetic angle reversals with theSignal Processor; programming the Programmable Gain Amplifier with theSignal Processor to optimize the signal gain in order to prevent voltageand current signal clipping; and controlling the PWM drive module withthe Signal Processor to control the amplitude, magnetic angle andreversal frequency applied to the electric motor (ACIM).
 2. A methodaccording to claim 1, comprising: controlling the boost converter withthe Signal Processor to limit/throttle the maximum power drawn from thesingle-phase AC source and the power delivered to the large energystorage device to maximally charge the energy storage device.
 3. Amethod according to claim 1, comprising controlling the series ofswitches (IPM) with a cross conduction preventer (CCP) to preventcrowbar of the DC Buss by adding dead-time to the PWM signals andinterlocking out unsafe PWM conditions, and controlling the CCP with thePWM drive module to pass through only safe PWM drive conditions.
 4. Amethod according to claim 1, comprising controlling the charging of theat least one energy storage device with the boost converter to a maximumworking voltage, sending an enable signal to the PWM drive to beginburst output from the Signal Processor, and sampling a stream ofmeasured voltage and/or currents of at least one of the motor legsduring burst output with a voltage transducer and a current transducerrespectively, which converts from analog to a digital A/D Converterdigital number with the A/D Converter.
 5. A method according to claim 4,comprising adjusting the PWM drive with a set point level and measuredvoltage and/or current to maintain a desired burst level in order tocompensate for sinking voltage of the at least one energy storage deviceapplied to the programmed voltage and/or current level applied to themotor with the Signal Processor: recording the stream of digital numberswith the Signal Processor; and calculating, at the end of each burst,rotor characteristics that include impedance, admittance, instantaneouspower, voltage and currents for the previously applied magnetic testangle with the Signal Processor.
 6. A method according to claim 1,comprising: recharging the at least one energy storage device with theboost converter until a maximum working voltage is attained, advancingthe magnetic angle by N degrees to measure the response of each set ofrotor bars that are in the line given magnetic angle and verify theresponse is the same for all magnetic angles with the Signal Processor,repeating the burst test N number of times until a full rotation ofmagnetic angles are tested and recorded with the Signal Processor,verifying, with the Signal Processor, rotor impedance versus magneticangle of the full rotation in order to check for failure, anddetermining failure by identifying a shift in measured stator'simpedance/admittance, harmonic or sub-harmonic level for any of thegiven magnetic angles by the Signal Processor.
 7. A system formagnetic/impedance burst testing of electric motors to determine brokenrotor bar defect, the system being encased in a portable tester andcomprising: a Signal Processor; a single-phase power source VAC; an ACto DC boost converter connected to the power source; at least one energystorage device connected to the AC to DC boost converter; a Pulse WidthModulated drive module (PWM) connected to the at least one energystorage device; and a series of at least three switches (IPM) usingswitch/level boost-type PWM rectification, the IPM connected to both the3 legs of the large electric motor and the PWM drive, wherein the PWM isprogrammed with a desired duration of output burst by the SignalProcessor; the PWM is programmed with an initial magnetic test angle bythe Signal Processor, the PWM is programmed with a test frequency formagnetic angle reversals by the Signal Processor; the programmable GainAmplifier is programmed by the Signal Processor to optimize the signalgain in order to prevent voltage and current signal clipping; and thePWM is controlled by the Signal Processor to control the amplitude,magnetic angle and reversal frequency applied to the electric motor(ACIM).
 8. A system according to claim 7, wherein: the boost converteris controlled by the Signal Processor to limit/throttle the maximumpower drawn from the single-phase AC source and the power delivered tothe large energy storage device to maximally charge the energy storagedevice.
 9. A system according to claim 7, wherein: the series ofswitches IPM is controlled by a cross conduction preventer (CCP) toprevent crowbar of the DC Buss by adding dead-time to the PWM signalsand interlocking out unsafe PWM conditions, the CCP is controlled by thePWM drive module to pass through only safe PWM drive conditions.
 10. Asystem according to claim 7, wherein: the charging of the at least oneenergy storage device is controlled by the boost converter to a maximumworking voltage; an enable signal to the PWM drive to begin burst outputis sent from the Signal Processor; and a stream of measured voltageand/or currents of at least one of the motor legs during burst outputare sampled with at least one voltage transducer and at least onecurrent transducer respectively, which converts from analog to a digitalA/D Converter digital number with the A/D Converter.
 11. A systemaccording to claim 10, wherein: the PWM drive is adjusted with a setpoint level and measured voltage and/or current to maintain a desiredburst level in order to compensate for sinking voltage of the at leastone energy storage device applied to the programmed voltage and/orcurrent level applied to the large electric motors with the SignalProcessor, the stream of digital numbers are stored within the SignalProcessor, at the end of each burst, rotor characteristics that includeimpedance, admittance, instantaneous power (I squared r), voltage andcurrents for the previously applied magnetic test angle are calculatedby the Signal Processor.
 12. A system according to claim 7, wherein: theat least one energy storage device is recharged by the boost converteruntil a maximum working voltage is re-attained; the magnetic angle isadvanced by N degrees to measure the response of each set of rotor barsthat are in the line given magnetic angle and verify the response is thesame for all magnetic angles with the Signal Processor; the burst testis repeated N number of times until a full rotation of magnetic anglesare tested and recorded with the Signal Processor; the Signal Processorverifies the rotor impedance versus magnetic angle of the full rotationin order to check for failure, and wherein broken rotor bar defect isdetermined when a shift in measured stator's impedance/admittance,harmonic or sub-harmonic level for any of the given magnetic angles isidentified by the Signal Processor.